The present invention pertains to tufted carpeting with improved tuft bind and cracking resistance characteristics. More particularly, the present invention pertains to reactive polyurethane formulations which can be used to prepare tufted carpet with improved tuft bind while retaining good carpet feel and resistance to cracking.
Tufted carpeting is manufactured by tufting yarns into a woven primary backing. The tufts are secured by applying at least one adhesive formulation to the primary backing side of the carpet/primary backing (xe2x80x9cgreige goodxe2x80x9d). In the past, SBR latexes have seen widespread use as adhesives for such purposes. However, such latexes have numerous drawbacks. First, neither the hydrolytic stability nor the durability of the cured elastomer is entirely satisfactory. Second, as the latex is applied in the form of an aqueous dispersion, considerable energy is expended in evaporating the aqueous component.
Polyurethanes have been considered as alternatives to SBR latex. Polyurethanes, in general, exhibit greater chemical and physical stability as compared to SBR latexes. Furthermore, polyurethanes may be applied either as an expandable or as a frothed foam, and may perform the dual function of tuft binding and cushioning. However, acceptable polyurethane systems have been difficult to formulate to achieve balanced properties. For example, tuft bind is known to be improved by increasing the hard segment content of the polyurethane polymer. However, increased hard segment content decreases the elastomer elongation, and alters both the feel of the carpet as well as its resistance to xe2x80x9ccrackingxe2x80x9d when rolled.
U.S. Pat. Nos. 4,696,849 and 4,853,054 attest to the difficulties experienced in preparing polyurethane carpet backings. In U.S. Pat. No. 4,696,849, for example, improvements in the tuft bind are achieved by use of two distinct high primary hydroxyl polyols, one having an actual functionality of 1.4-1.95 and a second having an actual functionality greater than 2.05, admixed such that the average functionality is within the very narrow range of 2.00xc2x10.03. Tuft bind is said to be increased, but no comparative formulations are included to verify any increase. In the U.S. Pat. No. 4,853,054 patent, blends of polyoxyalkylene polyether diols and triols, each having an equivalent weight between 1000 Da and 5000 Da, and the blend having an average actual functionality between 1.8 and 2.2, are used in conjunction with a polyisocyanate having a functionality between 1.9 and 2.4. Carpet splits are said to be reduced by the latter formulations, although the effect on tuft bind is unclear. When precoat adhesives are used, the average actual polyol blend functionality range is yet more narrow.
In general, it has been found that in order to be suitable for use as a carpet backing adhesive, the elongation of the polyurethane is desirably greater than 60%, with higher values more desirable, although the range between 40% and 60% may be acceptable for certain carpet styles and the degree of bending expected. Elongations lower than 60% often result in excessive cracking when the carpet is rolled or bent, for example during installation. Elongation less than 40% is clearly unacceptable. The lower acceptable limit for tuft bind is approximately 12 lbs, again with higher values much desired. As tuft bind is influenced by numerous factors such as the yarn denier, the nature of the backing, and the number of tufts per inch, limiting the polyurethane formulation window to resin components with functionalities close to two unacceptably limits the formulation window and the carpet properties which may be achieved.
It would be desirable to increase the tuft bind in polyurethane-backed carpeting. It would be further desirable to increase tuft bind without decreasing elongation of the polyurethane polymer. However, the competing effects of increasing the hard segment content, necessary to increase tuft bind, and increasing elongation which requires decreased high hard segment content, have thus far been unable to be reconciled.
It has now been surprisingly discovered that increases in tuft bind and elongation may be achieved by substituting 2-methyl-1,3-propanediol for all or part of the chain extender portion of polyurethane carpet backing adhesives, and that improvements in elongation and hence, cracking resistance, can be obtained by substituting low unsaturation polyols for all or part of the polyol component. The use of low unsaturation polyols allows the hard segment content to be raised, thus increasing tuft bind. Surprisingly, use of low unsaturation polyols does not require that a polyol functionality close to 2 be maintained. Preferably, 2-methyl-1,3-propanediol and low unsaturation polyol components are used simultaneously to provide both exceptional tuft bind and elongation.